Misfiring at 5,500 rpm or higher with little to no engine load - Page 4 - BMW M5 Forum and M6 Forums
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post #31 of 47 Old 11th April 2019, 06:26 PM
technician117
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Change the filter for sure but it probably won't fix the problem. I still think it might be the pump combined with a dirty fuel filter making it work harder than it can handle. Have you checked codes since reporting it was "better" with a full tank of fuel? Curious if they are the same misfire codes. Everyone is assuming they are the same since last reported, but the car drove better for a while since then.

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post #32 of 47 Old 11th April 2019, 06:52 PM Thread Starter
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LOL. You’re right about adaptations. I should have given them time to calibrate. But I’m curious as to what you think fixed the problem? The 02 sensors?

I’m wondering if the full tank of gas is masking a weak fuel pump.
Your problem existed at a very low demand for fuel, but that is not to say the frequency was just right to make a dirty injector fire incorrectly.



That said changing out your fuel filter is a no brainer because they are not life time. I would wait until you decide on the pump, because the best is to change the fuel pump then run the car then change the fuel filter, the extra flow from the new pump will wash more crud to the filter. Just a personal thing but I always change the filter 50 miles or so after a pump change even if the filter is new, because all the extra crud will make it old fast.



We will never know what the cause or fix was because that chance is gone. 10 miles of a injector cleaner could clean out a marginally dirty injector, but from reading this board for so many years 1 and 6 seem to be strange indicators of small vanos issues. I think it is 6 and 1 is a ghost. They are opposite cyls in the firing order and we see a ghost code as the real misfire code is generated. No idea why,I have just seen it often, but sometimes it is the cyl 3 before.
That’s a great point about doing the fuel pump before the filter. We still have a chance to figure out what the problem/cause is- car is still acting up. I got it to misfire yesterday with 3/4 tank left.

For now I will just keep driving and burning gas, hoping it’s just dirty injectors. I took your advice from a different thread- bought a case of Techron and Lucas fuel injector/upper cylinder head cleaner.

I was wondering if 1 and 6 were companion cylinders, not sure knowing that tells us anything LOL. My brain is fried with this car.

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Change the filter for sure but it probably won't fix the problem. I still think it might be the pump combined with a dirty fuel filter making it work harder than it can handle. Have you checked codes since reporting it was "better" with a full tank of fuel? Curious if they are the same misfire codes. Everyone is assuming they are the same since last reported, but the car drove better for a while since then.
The car did drive better for a while but now I can get it to misfire at high rpm on command like before. Fault codes are exactly the same-

C4- Misfire Cylinder #1
C9- Misfire Cylinder #6
CC- Misfire multiple cylinders
95- Misfire w/ empty fuel tank
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post #33 of 47 Old 11th April 2019, 09:08 PM
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I would like to make another suggestion. Remove and take a look at your crank position sensor (you can do it in 5 minutes without lifting the car, 5 or 6mm allen wrench is all it takes) and see if the flywheel is hitting the sensor. I had a very similar issue which I couldn't figure out, only would happen under load at high RPM in 2nd gear. Once I removed the crank sensor it was clear that my crank sensor was hitting the flywheel because it was missing the spacer. I don't know why it wasn't a problem at low RPM, but it only occurred above 5500 RPM or so.
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post #34 of 47 Old 11th April 2019, 10:15 PM
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One more idea that I remembered that can be helpful here. Specifically, there is a possibility that you have a broken wire somewhere and the engine twisting under torque is causing an electric disconnection. The way to test it is open the hood and quickly hit the gas with the engine in neutral. See which direction the engine moves under the hood. Remove the underbelly pan, put a jack on one side of the engine with a piece of wood, and now try to move the engine a bit while it is idling. Keep a close eye on the fan to make sure that it doesn't hit the fan shroud. As long as the fan doesn't hit the shroud I think you are fine. If moving the engine causes misfires, then you at least know that it is a wiring problem and can then start moving individual wires to try to further pinpoint the problem.
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post #35 of 47 Old 11th April 2019, 10:52 PM Thread Starter
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I would like to make another suggestion. Remove and take a look at your crank position sensor (you can do it in 5 minutes without lifting the car, 5 or 6mm allen wrench is all it takes) and see if the flywheel is hitting the sensor. I had a very similar issue which I couldn't figure out, only would happen under load at high RPM in 2nd gear. Once I removed the crank sensor it was clear that my crank sensor was hitting the flywheel because it was missing the spacer. I don't know why it wasn't a problem at low RPM, but it only occurred above 5500 RPM or so.

Thanks for the suggestion, great tip. This is what I found. Looks like flywheel has been rubbing against the crank sensor, ever so slightly. Now if this fixes the problem is another question. I can see the DME thinking there was a misfire if it isn't getting a clean, correct engine speed for sure.
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post #36 of 47 Old 12th April 2019, 08:56 AM
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You need to do a search for some other pics of crank sensors. There is a mark on them from the factory you need to compare. Although that one is clean in one spot, says something.
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post #37 of 47 Old 12th April 2019, 02:12 PM
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At this point you just need to figure out some way to move the crank sensor out just a bit. If you can't get a metal gasket quickly, you can make a few paper gaskets from regular paper just to temporarily move the sensor away from the flywheel and then go test it out. Paper gaskets probably aren't a good idea over a long term, but will work well enough for you to get a definitive answer whether this is the problem or not.
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post #38 of 47 Old 13th April 2019, 02:23 AM Thread Starter
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At this point you just need to figure out some way to move the crank sensor out just a bit. If you can't get a metal gasket quickly, you can make a few paper gaskets from regular paper just to temporarily move the sensor away from the flywheel and then go test it out. Paper gaskets probably aren't a good idea over a long term, but will work well enough for you to get a definitive answer whether this is the problem or not.

I'm 99% sure this was the problem with my car. The special plate (#9 in the picture) between the crank sensor and the bell housing was missing on my car. Because of this the sensor was rubbing the flywheel (apparently only at 5500+ rpm). The DME wasn't receiving a good crank signal at high rpm and thought the car was misfiring (even though it wasn't), so it was throwing misfire codes and cutting fuel.


I did what you suggested and just added a washer between the tranny and sensor as you can see in the picture.


I just drove for miles and miles between 5,500-6,500 rpm (obviously watching oil temp), no issues whatsoever.


Hopefully it stays that way.
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post #39 of 47 Old 13th April 2019, 03:20 AM Thread Starter
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You need to do a search for some other pics of crank sensors. There is a mark on them from the factory you need to compare. Although that one is clean in one spot, says something.

You're right about the mark from the factory- there is a groove in the plastic that is normal. I knew the sensor rubbing the flywheel was a problem, just thought it would be a problem at any engine speed. I guess the flywheel/clutch assembly flexes just enough at 5,500 rpm to start touching the tip of the sensor- especially since my spacer was missing.
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post #40 of 47 Old 13th April 2019, 03:53 AM
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At this point you know the solution. Buy the proper BMW spacer #9 and if you want to go all out, but a new crank position sensor, although that is not really necessary. If it runs fine now, then little scraping of the crank sensor isn't impacting its performance.
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